Modulating means



Jam, 79 w36, R, HOFER ET AL.

MODULATING MEANS Filed May 13, 1952 INVENTOR RUDOLF HOFER WILHELM U ERERBY ATTORNEY Patented Jan. 7, 1936 UNITED STATES PATENT CFFICEMODULA'IING MEANS tion of Germany Application May 13, 1932, Serial No.611,049 In Germany May 18, 1931 Claims.

This invention relates to a method of and arrangement for selectiveamplitude or phase modulation with Variable modulation.

The object of the present invention is to pro- 5 vide a new and improvedmethod of and means for producing phase or amplitude mddulatedoscillations, or both.

The manner in which this object is accomplished will be understood byreading of the l0 following description, and therefrom when read withthe drawing, in which:

Figure 1 is a curve illustrating the invention; while,

Figure 2 is any embodiment of the modulator. In the use and operation ofa transmitter or generator Valve the demand frequently arises to be ableto vary the -degree of modulation after modulation has been eected, orelse to be able to generate phase-modulated oscillations rather thanamplitude-modulated waves.

Figure 1, by way of example, shows a modulation curve of a generatorValve which presents a rectilinear portion only in its middle. In thepresence of high modulations undesirable distortions are bound to ariseowing to the curvature or knees of the curve. Now, in order that a highmodulation may be secured also in the presence of a modulation curve ofa kind as here shown, a more or less large part of the carrier wave,according to the present invention, is to be taken away (removed),whereas the size of the sidebands remains unaltered. What is essentialin this connection is that the phase of the added wave should be inexact phase coincidence with the phase of the carrier wave. But if anoscillation is added to the carrier wave having a different phaseposition then the ensuing oscillation results in a component at rightangles to the originalcarrier wave which, together with the sidebands,causes phase modulation. In other words, if energy including a side bandresulting from amplitude modulation is combined with a new carrier ofthe same frequency as the original carrier or the original carrier andthe phase of the new carrier or the original carrier is advanced orretarded with respect to the side band, a resultant will be obtainedwhich lies between the side band and new carrier. Now, if the signalvaries the 50 amplitude of the carrier the combined side band will varyand the position of the resultant relative to the side band and thecarrier will shift. This is phase modulation. For the production of purephase modulation care must be taken so 55 that the original carrier Wavewill be entirely extinguished and that only a component at right anglesthereto remains.

One embodiment of this basic idea. of the present invention is shown asincorporated in the circuit scheme Figure 2. Referring to the same, 5 Idenotes a separately controlled thermionic oscillation amplier excitedby generator 2 through windings T, or a generator valve whoseoscillations` as Well known in the art, are modulated in amplitude, e.g., by acting upon the grid 10 biasing potential, it being understoodthat recourse could be had also to some other mode of modulation such asby acting upon the plate potential.v The modulated oscillations are fed,for instance, to the points w, b, of a balanced bridge l5 3, whereas atthe points c, d, of the said bridge, there is suitably applied anunmodulated oscillation derived from the pilot generator 2. Byconvenient tuning of the circuit 4 and proper coupling of the coil 5 tothe pilot generator 2, the 20 amplitude and phase of the addedoscillation may be adjusted at will. Due to the combining of the carrierand side band energy there results, as pointed out hereinbefore, anoscillation, varied A in degree of modulation, or phase-modulated. 25

This resultant modulation is derivable at each of the four arms of thebridge, for instance, in arm a, d, from whence it may be utilized asshown.

In the rectification of a modulated oscillation of higher degree ofmodulation it is known to be 30 diiiicult to suppress non-lineardistortion of the audio frequency. In this instance, it is possible todiminish the degree of modulation by the addition of a carrieroscillation under proper phase conditions, whereby the rectifier effectis im- 35 proved both in linear detectors, as well as in detectorsoperating on the basis of a square law.

Having thus described our invention and the operation thereof, what weclaim is:

1. In a system for producing signal modulated 40 waves of substantiallyconstant amplitude, a thermionic tube having input and outputelectrodes, a source of high frequency oscillations connected with theinput electrodes thereof, a source of signal potentials connected withsaid 45 input electrodes, a bridge circuit, a circuit coupling opposedpoints on said bridge circuit to the output electrodes of said tube, aseparate circuit including amplitude and phase regulating elementscoupled between said high frequency source and another pair of opposedpoints on said bridge circuit, and a load circuit connected to saidbridge circuit.

2. An arrangement for the selective use of amplitude modulation andphase modulation with a variable degree of' amplitude modulation andphase modulation comprising, a thermionic generator, a thermionicamplitude modulator coupled to said generator, an output circuit coupledto said modulator, said output circuit comprising a bridge having fourarms, each arm of which comprises impedance, a coupling between onediagonal of said bridge and the output of said modulator, a circuitincluding phase shifting means coupled between said generator and theother diagonal of said bridge circuit, and a. work circuit coupled withone arm of said bridge.

3. In a signalling system, a thermionic modulator tube having a. sourceof high frequency oscillations and a source of modulating potentialscoupled to its input electrodes to amplitude modulate said highfrequency oscillations in said tube, a bridge circuit having onediagonal inductively coupled with the output electrodes of saidmodulator tube, a circuit for impressing oscillations of a frequencyequal to the frequency of the oscillations from said source of highfrequency oscillations on the other diagonal of said bridge circuit,means in said last named circuit for adjusting the phase and amplitudeof the impressed oscillations to oppose and diminish the carrierfrequency component in the energy of said bridge circuit resulting fromsaid modulation to thereby increase the degree of modulation and toreduce distortion in the signal modulated wave, and a load circuitcoupled to one arm of said bridge circuit.

4. Means for impressing amplitude and phase modulations on a, carrierwave and for varying the amount of either of said types of modulationfrom substantially zero to maximum While varying the other of said typesof modulation in the opposite direction comprising, a thermionic tubehaving anode, cathode and grid electrode, a circuit for applying carrierwaves to be modulated and signal waves for such modulation to the gridand cathode of said tube, an output circuit connected between the anodeand cathode of said tube, a bridge circuit including four arms eachhaving an impedance, a circuit coupling opposed nodal points on saidbridge to said output circuit, a circuit including tunable reactancesconnected to another pair of opposed nodal points on said bridge, saidlast named circuit including means on Which said carrier wave may beimpressed in 20 varying amounts, and a utilization circuit connectedwith the impedance in one of the arms of said bridge.

5. Means as set forth in claim 4 in which said utilization circuitcomprises a thermionic tube having its input electrode connected to theimpedance of one of said arms.

WILHELM KUMMERER. RUDOLF HOFER.

